The subject invention relates broadly to a cable safety device for monitoring the condition of a cable wrapped around a cable drum and more particularly, but not by way of limitation, to the monitoring of a cable on a cable drum used in raising and lowering overhead doors.
In the operation of residential and industrial overhead doors used for garages, warehouses, and the like, the overhead doors are counterbalanced through the use of a helically wound torsion spring. The spring transmits a torque equal to the weight of the door. A properly counterbalanced door may be raised and lowered with only a force sufficient to overcome the rolling friction of the rollers attached to the door.
In larger electrically operated doors, the door is raised by introducing a force on the cable sufficient to overcome the weight of the door. The door is lowered by gravity. If a door should be temporarily restrained when it is lowered, the cable on the drum may become loose and disengaged from around the drum. If the cable becomes disengaged and the restraint on the door is small, the door will fall. When the door falls, the cable often will not hold the free falling weight of the door thereby causing the door to crash on the floor. The falling of a large overhead door may cause damage to the door and danger to the personnel working near the door. The subject invention provides a means for eliminating this dangerous condition.
Prior to the subject invention, there has been no apparatus for alerting the operator of overhead doors that the door cable on the drum has become disengaged or unravelled and maintenance on the door is required.